Information recording medium and information reproducing apparatus

ABSTRACT

There is provided an information recording medium and an information reproducing apparatus capable of carrying out information reproduction and tracking control by utilizing near-field light. A data bit  12  of a convex having a section orthogonal to a tracking direction in a triangular shape is formed on an information recording medium  3  as an information unit, by scattering near-field light formed at a reproducing probe  1  at inclined faces of the data bit  12  with directionalities, fluxes of reflected and scattered light thereby are detected by reproduced light detectors  6  and  7  arranged symmetrically in a left and right direction relative to a central axis of the reproducing probe  1  along the tracking direction, a differential signal between the detected signals is outputted by a difference circuit  20  and an actuator  22  is driven by the differential signal via a tracking signal forming circuit  21  and a position of the reproducing probe  1  is controlled to carry out the tracking control.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of copendingInternational Application Ser. No. PCT/JP99/03638, filed on Jul. 6, 1999claiming a priority date of Jul. 7, 1008, and published in a non-Englishlanguage.

TECHNICAL FIELD

The present invention relates to an information recording medium whichis reproducible by utilizing near-field light and an informationreproducing apparatus for reproducing information recorded on theinformation recording medium at high density, particularly to aninformation recording medium and an information reproducing apparatusenabling tracking control.

BACKGROUND OF THE INVENTION

Currently, many of information reproducing apparatus carry outreproduction of information with an information medium of a magneticdisk or an optical disk as an object, particularly, CD (Compact Disk)which is one of optical disks is widely used as a medium enablinginformation recording at high density and mass production at low costand recording a large capacity of information. A surface of CD is formedwith pits each having a size of about a wavelength of laser beam used inreproduction and a depth of about a quarter of the wavelength andreading operation utilizing interference phenomenon of light is carriedout.

In reading recorded information from an optical disk represented by CD,generally, there is utilized a lens optical system used in an opticalmicroscope. In this case, when an information recording density isincreased by reducing a size of the pit or a track pitch thereof, adeadlock is reached by the problem of diffraction limit of light inwhich a spot size of laser beam cannot be made equal to or smaller thana half wavelength and an information recording unit cannot be reduced toa size smaller than the wavelength of laser beam.

Further, not only in CD but also in optical recording disks recordedwith information by a magneto-optical recording system and a phasechange recording system, record and reproduction of information at highdensity is realized by a very small spot of laser beam and accordingly,the information recording density is restricted by a diameter of thespot provided by converging laser beam.

Hence, in order to break the restriction imposed by the diffractionlimit, there is proposed an information reproducing apparatus using anoptical head provided with a very small aperture having a diameter equalto or smaller than a wavelength of laser beam utilized for reproduction,for example, a diameter of about {fraction (1/10)} of the wavelength andutilizing near-field light (including both of near-field light andfar-field light) formed at the very small aperture portion.

Originally, as an apparatus utilizing near-field light, there isprovided a near-field microscope using a probe having theabove-described very small aperture and the near-field microscope isutilized in observing a very small surface structure of a sample. As oneof systems of utilizing near-field light in a near-field microscope,there is provided a system in which a very small aperture of a probe anda surface of a sample are made proximate to each other such that adistance therebetween is equal to about a diameter of the very smallaperture of the probe and by introducing propagating light via the probetoward the very small aperture of the probe, near-field light is formedat the very small aperture (illumination mode). In this case, scatteredlight produced by interaction of the formed near-field light and thesurface of the sample, is detected by a scattered light detecting systemwith an intensity and a phase reflecting a fine structure of the surfaceof the sample and there is enabled observation having high resolutionwhich cannot be realized by a conventional optical microscope.

Further, as other system of a near-field microscope utilizing near-fieldlight, there is provided a system in which a sample is irradiated withpropagating light to thereby localize near-field light on the surface ofthe sample and a very small aperture of a probe is made proximate to thesurface of the sample to a degree of a diameter of the very smallaperture of the probe (collection mode). In this case, scattered lightproduced by interaction of the localized near-field light and the verysmall aperture of the probe, is guided to a scattered light detectingsystem via the very small aperture of the probe with an intensity and aphase reflecting a fine structure of the surface of the sample tothereby achieve observation with high resolution.

According to the above-described information reproducing apparatusutilizing near-field light, there are utilized these observation systemsin the near-field microscope and by unitizing the near-field light,there is enabled reproduction of information of an information recordingmedium recorded with information with higher density.

In order to realize reproduction of information recorded on theinformation recording medium with high density by utilizing theabove-described near-field light, there is needed a positioning controltechnology for moving the very small aperture portion of the probeconstituting an optical head to an arbitrary position on the informationrecording medium with high precision.

In the case of a magnetic disk apparatus, generally, as positioningcontrol, there are adopted a servo face servo system and a sector servosystem. The servo face servo system is a method in which one face in aplurality of disk faces is used exclusively for servo, a magnetic headfor servo is positioned relative to the servo face and a remaining diskface and a magnetic head are used for data. Further, the sector servosystem is a method in which servo information is embedded sporadicallyon data face and by using the servo information detected discretely, amagnetic head is positioned on data tracks.

However, it is difficult to apply positioning control adopted in thesemagnetic disk apparatus to positioning control in respect ofreproduction of a high density information recording medium bynear-field light. For example, according to the above-described servoface servo system, positional accuracies of a head for servo and a headfor data are determined by mechanical accuracies and accordingly, thereis a case in which a positional shift is produced between the both headsby a difference in temperature distribution and the system is notsuitable for being adopted as positioning control in respect of aninformation recording medium with high density formation.

Further, according to the above-described sector servo system, althoughthere causes no positional shift of heads caused by the difference inthe temperature distribution which is problematic in the servo faceservo system, at a design stage of a control system, the control systemneeds to deal with as a discrete value system different from aconventional continuous system and in the case of an informationreproducing apparatus utilizing near-field light, there is needed highaccuracy positioning with regard to an information recording medium withparticularly high density formation and accordingly, it is notpreferable to use such a complicated control system.

Meanwhile, according to an optical disk apparatus, aspositioning,control methods, particularly as tracking error detectingmethods, there are adopted a three beam method, a push-pull method and aprewobbling tracking error detecting method. The three beam method is amethod in which beam from a laser diode is divided into a total of threebeams of a 0-th order beam (main beam) for record and reproduction andtwo 1-th order beam (sub beam) for tracking by a diffracting grating,two of the sub beams are slightly shifted from a center of a guidegroove provided on an optical disk, fluxes of reflected beam from bothof them are received by two light receiving faces of an optical detectorand an objective lens is controlled by a differential signal thereof.

Further, the push-pull method is a method in which fluxes of reflectedbeam of beam irradiated to guide grooves provided on an optical disk aredetected by a two split detector and a differential signal providedthereby constitutes a track error signal to thereby control an objectivelens. The prewobbling tracking error detecting method is a method inwhich a set of two long pits (prewobbling marks) A and B are previouslyarranged on an optical disk to slightly shift from each other in thedisk radius direction relative to a center of a track and a change in anamount of fluxes of reflected beam from the pits A and B produced intracing the center of the track by a light spot, constitutes a trackerror signal to thereby control an objective lens.

The above-described tracking error detecting methods of the optical diskapparatus are methods in the case in which both of irradiated light tothe pit formed on the optical disk and reflected light reflected therebyare dealt with as propagating light (far-field) and a devise is neededwhen the methods are applied to detection of nonpropagated beam(near-field) such as near-field light and reflected and scattered lightthereof. Further, particularly, in a case of an information recordingmedium enabling reproduction by utilizing near-field light, aninformation recording unit can be determined not only by recess andprojection information as in a pit formed on a conventional optical diskbut also a difference in an optical property and accordingly, there isrequested an information reproducing apparatus for carrying out opticalhead positioning control, particularly, tracking in order to reproducesuch an information recording medium.

It is an object of the invention to provide an information recordingmedium and an information reproducing apparatus for realizingreproduction of information having high reliability in respect of aninformation recording medium recorded with information at high density,particularly, tracking by a simple constitution.

DISCLOSURE OF THE INVENTION

In order to achieve the above-described object, according to a firstaspect of the invention, there is provided an information recordingmedium characterized in that in an information recording medium in whichinformation to be reproduced by a reproducing probe provided with a verysmall aperture for forming near-field light is formed on a surface ofthe medium, wherein a unit of the information is constructed by astructure in which inclined faces or curved faces are providedsymmetrically in a left and right direction relative to a readingdirection and the left and right inclined faces intersect with eachother or the left and right curved faces coincide with each other.

According to the first aspect of the invention, the unit of informationis constructed by the structure in which the inclined faces or thecurved faces are provided symmetrically in the left and right directionwith the reading direction as the central axis and accordingly,directionalities can be given to fluxes of reflected light which arereflected when the unit of information is irradiated with fluxes oflight and a difference between intensities of the fluxes of reflectedlight can be unitized as a signal for tracking.

Further, according to a second aspect of the invention, there isprovided the information recording medium according to the first aspect,characterized in that the unit of the information is constituted by asection orthogonal to the reading direction in a triangular shape.

According to the second aspect of the invention, the section of the unitof information orthogonal to the reading direction is formed in thetriangular shape and accordingly, when the unit of information isirradiated with fluxes of light, the fluxes of light can efficiently bereflected at the inclined faces of the unit of information, further, thedirectionalities can be given to fluxes of the reflected light andaccordingly, the difference between the intensities of the fluxes ofreflected light can be utilized as a signal for tracking.

Further, according to a third aspect of the invention, there is providedthe information recording medium according to the first aspect,characterized in that the unit of the information is constituted by asection orthogonal to the reading direction in a semicircular shape.

According to the third aspect of the invention, the section of the unitof the information orthogonal to the reading direction is formed in thesemicircular shape and accordingly, when the unit of information isirradiated with fluxes of light, the fluxes of light can efficiently bereflected at the curved faces of the unit of the information, further,the directionalities can be given to fluxes of the reflected light andaccordingly, the difference between the intensities of the fluxes ofreflected light can be utilized as a signal for tracking.

Further, according to a fourth aspect of the invention, there isprovided the information recording medium according to the second or thethird aspect, characterized in that the unit of the information isformed in a convex relative to a surface of the medium.

According to the fourth aspect of the invention, the unit of informationis constructed by a structure in which the unit of the information isprovided with the inclined faces or the curved faces symmetrically inthe left and right direction with the reading direction as the centralaxis and is formed in the convex relative to the surface of theinformation recording medium and accordingly, when the unit of theinformation is irradiated with fluxes of light which are shifted on theleft side, the fluxes of light can be reflected strongly in the leftdirection and when the unit of the information are irradiated withfluxes of light which are shifted on the right side, the fluxes of lightcan be reflected strongly in the right direction and accordingly, thedifference between the intensities of, fluxes of reflected light can beutilized as a signal for tracking.

Further, according to a fifth aspect of the invention, there is providedthe information recording medium according to the second or the thirdaspect, characterized in that the unit of the information is formed in aconcave relative to a surface of the medium.

According to the fifth aspect of the invention, the unit of informationis constructed by a structure in which the unit of the information isprovided with the inclined faces or the curved faces symmetrically inthe left and right direction with the reading direction as the centralaxis and is formed in the concave relative to the surface of theinformation recording medium and accordingly, when the unit ofinformation is irradiated with fluxes of light which are shifted to theleft, the fluxes of light can be reflected strongly in the rightdirection and when the unit of information is irradiated with fluxes oflight which are shifted to the right, the fluxes of light can bereflected strongly in the left direction and accordingly, the differencebetween the intensities of fluxes of the reflected light can be utilizedas a signal for tracking.

Further, according to a sixth aspect of the invention, there is providedthe information recording medium according to any one of the firstthrough the fifth aspects, characterized in that a metal reflecting filmis formed on the surface of the medium.

According to the sixth aspect of the invention, the metal reflectingfilm is formed on the surface of the information recording medium andaccordingly, fluxes of light irradiated to the unit of information canefficiently be reflected.

Further, according to a seventh aspect of the invention, there isprovided an information reproducing apparatus for reproducinginformation by a reproducing probe provided with a very small aperturefor forming near-field light, characterized in comprising an informationrecording medium in which a unit of the information is constructed by astructure in which inclined faces or curved faces are providedsymmetrically in a left and right direction relative to a readingdirection and the left and the right inclined faces intersect with eachother or the left and the right curved faces coincide with each other,and a control apparatus for detecting fluxes of reflected and scatteredlight produced by scattering the near-field light by the unit of theinformation at at least two positions symmetrical with each otherrelative to a central axis of the very small aperture along the readingdirection and controlling a position of the reproducing probe inaccordance with a detected signal.

According to the seventh aspect of the invention, by forming the unit ofthe information constructed by the structure in which the inclined facesor the curved faces are provided on the left and on the right with thereading direction as the central axis and with the central axis as a topportion, to the information recording medium and making the near-fieldlight formed at the very small aperture of the reproducing probeincident on the information unit, there can be formed fluxes of thereflected and, scattered light provided with the directionalities to theleft and to the right, the fluxes of reflected and scattered light aredetected at at least two-positions symmetrical with each other relativeto the central axis of the very small aperture and the position of thereproducing probe is controlled in accordance with the detected signaland accordingly, tracking control with high accuracy utilizing thenear-field light can be carried out.

Further, according to an eighth aspect of the invention, there isprovided an information reproducing apparatus for reproducinginformation by a reproducing probe provided with a very small aperturefor forming near-field light, characterized in comprising an informationrecording medium in which a unit of the information is constructed by astructure in which inclined faces or curved faces are providedsymmetrically in a left and right direction relative to a readingdirection and the left and the right inclined faces intersect with eachother or the left and the right curved faces coincide with each otherand a first and a second light detecting means arranged symmetricallywith each other in the left and right direction relative to a centralaxis of the very small aperture along the reading direction fordetecting fluxes of reflected and scattered light produced by scatteringthe near-field light by the unit of the information and outputtingdetected signals, difference calculating means for calculating adifference between a first detected signal outputted from the firstlight detecting means and a second detected signal outputted from thesecond light detecting means and outputting a differential signal,reproducing probe position controlling means for controlling a positionof the reproducing probe in accordance with the differential signal, andreproduced signal forming means for calculating to add the firstdetected signal and the second detected signal and forming a reproducedsignal.

According to the eighth aspect of the invention, by forming the unit ofthe information constructed by the structure in which the inclined facesor the curved faces are provided on the left and on the right with thereading direction as the central axis and with the central axis as a topportion, in the information recording medium and making the near-fieldlight formed at the very small aperture of the reproducing probeincident on the unit of the information, there can be formed fluxes ofthe reflected and scattered light provided with the directionalities tothe left and to the right, the fluxes of reflected and scattered lightare detected by the first and the second light detecting means arrangedat at least two positions symmetrical with each other relative to thecentral axis of the very small aperture, the differential signalindicating the difference between the first detected signal detected andoutputted by the first light detecting means and the second detectedsignal detected and outputted by the second light detecting means, isformed by the difference calculating means, positioning control of thereproducing probe in accordance with the differential signal can becarried out by the reproducing probe position controlling means andaccordingly, tracking control with high accuracy utilizing thenear-field light can be carried out. Further, the reproduced signal canbe formed by calculating to add the first detected signal and the seconddetected signal and accordingly, reproduction of the information cansimultaneously be carried out.

Further, according to a ninth aspect of the invention, there is providedthe information recording apparatus according to the seventh or theeighth aspect, characterized in that the reproducing probe comprises anoptical fiber provided with the very small aperture at a front endthereof.

According to the ninth aspect of the invention, as the reproducingprobe, there can be utilized a probe of an optical fiber type used in aconventional near-field microscope and accordingly, accumulatedtechnology of the near-field microscope can effectively be applied tothe information reproducing apparatus.

Further, according to a tenth aspect of the invention, there is providedthe information reproducing apparatus according to the seventh or theeighth aspect, characterized in that the reproducing probe is a probe ofa cantilever type provided with the very small aperture at a projectedportion thereof.

According to the tenth aspect of the invention, as the reproducingprobe, there can be utilized the probe of the cantilever-type used inthe conventional near-field microscope and accordingly, the accumulatedtechnology of the near-field microscope can effectively be applied tothe information reproducing apparatus.

According to an eleventh aspect of the invention, there is provided theinformation recording apparatus according to the seventh or the eighthaspect, characterized in that the reproducing probe is a plane probecomprising a plane substrate formed by being penetrated with a hole in ashape of an inverse cone to constitute the very small aperture by a topportion thereof and the first and the second light detecting means arearranged at the plane substrate.

According to the eleventh aspect of the invention, as the reproducingprobe, there can be utilized the plane probe arranged with the first andthe second light detecting means and accordingly, a simple apparatusconstitution can be realized with no need of adjusting positions of thefirst and the second light detecting means.

Further, according to a twelfth aspect of the invention, there isprovided the information reproducing apparatus according to the eleventhaspect, characterized in that the reproducing probe is the plane probearranged with a third and a fourth light detecting means for detectingthe fluxes of the reflected and scattered light at vicinities of thevery small aperture.

According to the twelfth aspect of the invention, as the reproducingprobe, there can be utilized the plane probe arranged with the first andthe second light detecting means and the third and the fourth lightdetecting means for detecting fluxes of the reflected and scatteredlight at vicinities of the very small apertures and accordingly, thereproduced signal having sufficient intensity can be detected by thefirst and the second light detecting means and the third and the fourthlight detecting means.

Further, according to a thirteenth aspect of the invention, there isprovided an information reproducing apparatus for forming near-fieldlight at an information recording medium and reproducing information bya reproducing probe for scattering the near-field light, characterizedin that fluxes of reflected and scattered light produced by scatteringthe near-field light produced at a unit of the information formed on theinformation recording medium by a front end portion of the reproducingprobe, are detected at at least two positions symmetrical with eachother relative to the front end portion of the reproducing probe and aposition of the reproducing probe is controlled in accordance with adetected signal.

According to the thirteenth aspect of the invention, the near-fieldlight produced at the unit of information of the information recordingmedium is scattered by the reproducing probe, fluxes of the reflectedand scattered light are detected at at least two positions symmetricalwith each other relative to the front end portion of the reproducingprobe, the position of the reproducing probe is controlled in accordancewith the detected signal and accordingly, tracking control with highaccuracy utilizing the near-field light can be carried out.

Further, according to a fourteenth aspect of the invention, there isprovided an information reproducing apparatus for forming near-fieldlight at an information recording medium and reproducing information bya reproducing probe for scattering the near-field light, characterizedin comprising a first and a second light detecting means arrangedsymmetrically with each other relative to a front end portion of thereproducing probe along a reading direction for detecting fluxes ofreflected and scattered light produced by scattering the near-fieldlight by a front end portion of the reproducing probe and outputtingdetected signals, difference calculating means for calculating adifference between a first detected signal outputted from the firstlight detecting means and a second detected signal outputted from thesecond light detecting means and outputting a differential signal,reproducing probe position controlling means for controlling a positionof the reproducing probe in accordance with the differential signal andreproduced signal forming means for forming a reproduced signal bycalculating to add the first detected signal and the second detectedsignal.

According to the fourteenth aspect of the invention, the near-fieldlight produced at the unit of the information of the informationrecording medium is scattered by the reproducing probe, fluxes of thereflected and scattered light are detected by the first and the secondlight detecting means arranged at at least two positions symmetricalwith each other relative to the central axis of the very small aperture,the differential signal indicating the difference between the firstdetected signal detected and outputted by the first light detectingmeans and the second detected signal detected and outputted by thesecond light detecting means, is formed by the difference calculatingmeans, position control of the reproducing probe in accordance with thedifferential signal can be carried out by the reproducing probe positioncontrolling means and accordingly, tracking control with high accuracyutilizing the near-field light can be carried out. Further, thereproduced signal can be formed by carrying out operation of adding thefirst detected signal and the second detected signal by the reproducedsignal forming means and accordingly, the information can simultaneouslybe reproduced.

Further, according to a fifteenth aspect of the invention, there isprovided the information reproducing apparatus according to thethirteenth or the fourteenth aspect, characterized in that thereproducing probe is formed in a wedge-like shape.

According to the fifteenth aspect of the invention, the reproducingprobe is formed in the wedge-like shape and accordingly, by reflectingthe near-field light produced at the unit of the information of theinformation recording medium by the two inclined faces constituting thewedge-like shape, the directionalities can be given to fluxes of thereflected light and accordingly, the difference between the intensitiesof the fluxes of reflected light can be provided further significantlyand tracking control with high accuracy utilizing the near-field lightand having high reliability can be carried out. Further, sufficientlylarge intensity can be provided to the reproduced signal by the fluxesof reflected light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an outline constitution of aninformation reproducing apparatus according to Embodiment 1.

FIG. 2 is a view for explaining operation of the information reproducingapparatus according to Embodiment 1.

FIG. 3 is a view for explaining operation of the information reproducingapparatus according to Embodiment 1.

FIG. 4 is a block diagram showing an outline constitution of aninformation reproducing apparatus according to Embodiment 2.

FIG. 5 is a view for explaining operation of the information reproducingapparatus according to Embodiment 2.

FIG. 6 is a view for explaining operation of the information reproducingapparatus according to Embodiment 2.

FIG. 7 is a view showing an example of a reproducing probe of theinformation reproducing apparatus according to Embodiments 1 and 2.

FIG. 8 is a view showing other example of a reproducing probe of theinformation reproducing apparatus according to Embodiments 1 and 2.

FIG. 9 is a block diagram showing an outline constitution of aninformation reproducing apparatus according to Embodiment 3.

FIG. 10 is a view showing a reproducing probe of the informationreproducing apparatus according to Embodiment 3.

FIG. 11 is a view for explaining operation of the informationreproducing apparatus according to Embodiment 3.

FIG. 12 is a view for explaining operation of the informationreproducing apparatus according to Embodiment 3.

BEST MODE FOR CARRYING OUT THE INVENTION

A detailed explanation will be given of embodiments of an informationrecording medium and an information reproducing apparatus according tothe invention as follows.

(Embodiment 1)

FIG. 1 is a block diagram showing an outline constitution of aninformation reproducing apparatus according to Embodiment 1. In FIG. 1,the information reproducing apparatus according to Embodiment 1 isconstituted by, a reproducing probe 1 for forming near-field light, aninformation recording medium 3 formed with data bits at high density,converging optical systems 4 and 5 for converging fluxes of reflectedand scattered light scattered by the data bits of the informationrecording medium 3, reproduced light detectors 6 and 7 for receivingfluxes of light converged by the converging optical systems 4 and 5 andoutputting electric signals, a difference circuit 20 for calculating adifference between the respective electric signals outputted from thereproduced light detectors 6 and 7, a tracking signal generator 21 forgenerating and outputting a tracking signal from the differential signaloutputted from the difference circuit 20, an actuator 22 for controllinga position of the reproducing probe in accordance with the trackingsignal outputted from the tracking signal generator 21 and an addingcircuit 23 for forming a reproduced signal by adding the respectiveelectric signals outputted from the reproduced light detectors 6 and 7.

The reproducing probe 1 is formed with a very small aperture 2 having asize equal to or smaller than a wavelength of laser beam 10 introducedfrom a laser beam source (not illustrated), for example, a diameter ofseveral tens nanometers and near-field light 11 is formed at the verysmall aperture 2 by introducing the laser beam 10. As the reproducingprobe 1, a probe used in a conventional near-field microscope can beutilized and is a probe enabling to form near-field light according tothe above-described illumination mode, for example, an optical fiberprobe comprising an optical fiber having a very small aperture at itsfront end and a surface coated by a metal, a cantilever-type opticalprobe having a very small aperture to which laser beam is guided via anoptical waveguide at its front end, a plane probe comprising a planesubstrate formed with a through hole in a shape of an inverse cone suchthat an apex thereof constitutes a very small aperture or the like.

The near-field light 11 formed at the vary small aperture 2 of thereproducing probe 1 is scattered by a data bit 12 of the convex shapeformed on a substrate of the information recording medium 3 andscattered light constitutes propagating light (hereinafter, referred toas reflected and scattered light) and is introduced into the convergingoptical systems 4 and 5. In this case, the converging optical systems 4and 5 each is constructed by a constitution of a converging lens or acollimating lens or the lens added with a light guide or an opticalfiber and converge the reflected and scattered light to the reproducedlight detectors 6 and 7 such that sufficiently detectably intensitiesare constituted. The reproduced light detectors 6 and 8 are, forexample, photodiodes or photomultipliers.

The converging optical systems 4 and 5 and the reproduced lightdetectors 6 and 7 are arranged at fixed positions relative to thereproducing probe 1 and are positioned relative to the informationrecording medium 3 along with the reproducing probe 1 particularly bypositioning control by the actuator 22. Therefore, it is preferable toconstitute a light reproducing head integrated with the reproducingprobe 1, the converging optical systems 4 and 5 and the reproduced lightdetectors 6 and 7 and the light reproducing head is subjected topositioning control by the actuator 22.

The information recording medium 3 is constructed by a structure inwhich a top portion of the data bit 12 for constituting an informationunit formed by combining two inclined faces symmetrically and in aconvex relative to a surface of the information recording medium 3,constitutes a central axis and the central axis coincides with a readingdirection by the reproducing probe 1 (hereinafter, referred to as atracking direction). That is, a section of the data bit 12 orthogonal tothe reading direction is formed in a shape of a ridge in a triangularshape as shown by FIG. 1 and the apex of the triangular shape isdisposed on the central axis of reading (central axis of tracking). Bypresence of the two symmetrical inclined faces, directionalities can begiven to fluxes of the reflected and scattered light of the near-fieldlight 11. Further, it is preferable for providing reflected andscattered light having a sufficient intensity to form a metal reflectingfilm on the surface of the information recording medium 3. Further, thereflection efficiency of the near-field light 11 can also be promoted byforming the information recording medium 3 per se by a metal.

Accordingly, by arranging a constitution comprising the convergingoptical system 4 and the reproduced light detector 6 and a constitutioncomprising the converging optical system 5 and the reproduced lightdetector 7 at positions symmetrical to each other relative to a centralaxis in parallel with a tracking direction of the very small aperture 2of the reproducing probe 1 (hereinafter, referred to as reproducingprobe central axis), fluxes of the reflected and scattered lightreflected in directions symmetrical with each other by the two inclinedfaces provided at the data bit 12 can be detected.

FIG. 2 is a view for explaining detection of reflected and scatteredlight when the reproducing probe 1 is arranged in a state in which thecentral axis of the reproducing probe and the tracking central axis arenot coincident with each other. In FIG. 2, the reproducing probe 1 isdisposed on the right side of the tracking central axis, that is, thetop of the data bit 12 and fluxes of reflected and scattered light 13and 14 are produced by interaction between the near-field light 11formed at the very small aperture 2 under the state and the data bit 12.

In FIG. 2, the near-field light 11 is significantly scattered by theright inclined face of the data bit 12 and the reflected and scatteredlight 13 is guided in the right direction depending on an angle ofinclination of the right inclined face. The reflected and scatteredlight 13 guided in the right direction is introduced into the convergingoptical system 5 and is inputted to the reproduced light detector 7.

Meanwhile, the near-field light 11 shows the largest intensity on thecentral axis of the reproducing probe and directly under the very smallaperture 2 and accordingly, on the left inclined face of the data bit 12disposed remote from the central axis of the reproducing probe, theintensity of the reflected and scattered light 14 provided by beingscattered becomes weaker than that of the reflected and scattered light13 on the side of the right inclined face. The reflected and scatteredlight 14 guided in the left direction is also introduced into theconverging light optical system 4 and is inputted to the reproducedlight detector 6.

Accordingly, in this case, the electric signal outputted at thereproduced light detector 7 is a signal larger than the electric signaloutputted at the reproduced light detector 6. These electric signals areinputted to the difference circuit 20 and the differential signal isformed there as mentioned above. The magnitude of the differentialsignal indicates a degree of shift of the reproducing probe 1 from thetracking central axis and the differential signal is converted into thetracking signal by being inputted to the tracking signal generator 21.The tracking signal is a signal for driving the actuator 22 and theactuator 22 controls the position of the reproducing probe 1 inaccordance with the tracking signal. For example, when the differencecircuit 20 carries out an operation of subtracting the electric signaloutputted from the reproduced light detector 7 from the electric signaloutputted from the reproduced light detector 6, in a state shown by FIG.2, the differential signal outputted from the difference circuit 20shows a negative value. Successively, the tracking signal generator 21interprets the negative differential signal as a signal for moving theactuator 22 to the left and outputs a tracking signal indicating themoving direction and a moving amount in accordance with the magnitude ofthe differential signal to the actuator 22. That is, the tracking signalgenerator 21 generates an actuator driving signal for correcting theshift between the reproducing probe 1 and the tracking central axis. Theactuator 22 moves the reproducing probe 1 in accordance with thetracking signal outputted from the tracking signal generator 21 andmakes the central axis of the reproducing probe and the tracking centralaxis coincide with each other. That is, tracking control in the leftdirection is carried out.

Further, although in FIG. 2, there is shown the case in which thereproducing probe 1 is disposed on the right side of the trackingcentral axis, when the reproducing probe 1 is disposed on the left sideof the tracking central axis, an operation reverse to theabove-described is carried out. That is, in that case, tracking controlin the right direction is carried out.

Further, in parallel with the above-described tracking processing, theelectric signal outputted at the reproduced light detector 7 and theelectric signal outputted at the reproduced light detector 6 areinputted to the adding circuit 23 where the adding operation is carriedout and are outputted as the reproduced signal. Thereby, presence orabsence of the data bit 12 directly under the very small aperture 2 isdetected.

FIG. 3 is a view for explaining detection of reflected and scatteredlight when the reproducing probe 1 is arranged such that the centralaxis of the reproducing probe and the tracking central axis coincidewith each other. In FIG. 3, the near-field light 11 formed at the verysmall aperture 2 produces fluxes of the reflected and scattered light 13and 14 by uniform interaction of the right inclined face and the leftinclined face of the data bit 12. That is, both of the fluxes of thereflected and scatted light 13 and 14 show substantially the sameintensity and the electric signals respectively outputted at thereproduced light detector 7 and the reproduced light detector 6 alsoshow substantially the same magnitude. Accordingly, no difference isproduced at the difference circuit 20 and positioning control in theactuator 22 is not carried out. That is, FIG. 3 represents a final stateafter the above-described tracking control has been carried out.

Further, although according to Embodiment 1, explained above, there isconstructed the structure in which the inclined faces are provided onthe left and on the right of the tracking central axis by constitutingthe section of the data bit recorded to the information recording mediumby the ridge in the triangular shape, for example, there may beconstructed a structure in which the section of the data bit isconstituted by a ridge in a semicircular shape and curved faces areprovided on the left and on the right of the tracking central axis.

Further, data may be read by constituting the information recordingmedium in a disk-like shape as in CD and rotating the informationrecording medium at high speed or data may be read by forming theinformation recording medium as a flat plate without being limited tothe disk-like shape and carrying out vector scanning by the reproducingprobe.

As has been explained above, according to the information recordingmedium of Embodiment 1, the data bit constituting the information unitis constructed by a structure in the convex in which the inclined facesor the curved faces are provided symmetrically in the left and rightdirection relative to the central axis of the reading direction(tracking direction) and accordingly, the directionalities can be givento fluxes of the reflected and scattered light produced by scatteringnear-field light by the data bit. Further, according to the informationreproducing apparatus of Embodiment 1, fluxes of the reflected andscattered light provided from the data bit of the above-describedinformation recording medium can be detected in two symmetricaldirections relative to the central axis of the reproducing probe and thetracking control of the reproducing probe can be carried out from thedifference between the two detected signals. Further, the near-fieldlight formed at the very small aperture of the reproducing probe isutilized as a signal for tracking control and accordingly, there isachieved tracking control at high accuracy accompanied by highpositional resolution. Further, the constitution of the apparatus can besimplified since the optical systems used in detecting fluxes of thereproduced signal and detecting the tracking signal are not separatedbut are unified.

(Embodiment 2)

FIG. 4 is a block diagram showing an outline constitution of aninformation reproducing apparatus according to Embodiment 2. In FIG. 4,the information reproducing apparatus according to Embodiment 2 isconstituted by the reproducing probe 1 for forming near-field light, aninformation recording medium 8 formed with data bits at high density,the converging optical systems 4 and 5 for converging fluxes ofreflected and scattered light scattered by the data bits of theinformation recording medium 8, the reproduced light detectors 6 and 7for receiving fluxes of light converged by the converging opticalsystems 4 and 5 and outputting electric signals, the difference circuit20 for calculating a difference between the respective electric signalsoutputted from the reproduced light detectors 6 and 7, the trackingsignal generator 21 for generating and outputting a tracking signal fromthe differential signal outputted from the difference circuit 20, theactuator 22 for controlling a position of the reproducing probe inaccordance with the tracking signal outputted from the tracking signalgenerator 21 and the adding circuit 23 for forming a reproduced signalby adding the respective electric signals outputted from the reproducedlight detectors 6 and 7.

The reproducing probe 1 is formed with the very small aperture 2 havingthe size equal to or smaller than the wavelength of the laser beam 10introduced from a laser beam source (not illustrated), for example, thediameter of several tens nanometers and the near-field light 11 isformed at the very small aperture 2 by introducing the laser beam 10. Ashas been explained in Embodiment 1, the reproducing probe 1 is a probeenabling to form near-field light by the above-described illuminationmode such as an optical fiber probe, a cantilever-type optical probe, aplane probe or the like.

The near-field light 11 formed at the very small aperture 2 of thereproducing probe 1 is scattered by a data bit 15 of a concave formed onthe information recording medium 8 and the scattered light constitutespropagating light (hereinafter, referred to as reflected and scatteredlight) and fluxes thereof are introduced into the converging opticalsystems 4 and 5. In this case, as has been explained in Embodiment 1,the converging optical systems 4 and 5 each is constructed by aconstitution of, for example, a converging lens or a collimating lens orthe like or the lens added with a light guide or an optical fiber andthe reproduced light detectors 6 and 7 are, for example, photodiodes,photomultipliers or the like.

The converging optical systems 4 and 5 and the reproduced lightdetectors 6 and 7 are arranged at fixed positions relative to thereproducing probe 1 and are positioned relative to the informationrecording medium 8 along with the reproducing probe 1 particularly bypositioning control by the actuator 22. Therefore, it is preferable toconstitute a light reproducing head integrated with the reproducingprobe 1, the converging optical systems 4 and 5 and the reproduced lightdetectors 6 and 7 and the light reproducing head is subjected topositioning control by the actuator 22.

The information recording medium 8 is constructed by a structure inwhich a top portion of the data bit 15 for constituting an informationunit formed by combining two inclined faces symmetrically and in aconcave relative to a surface of the information recording medium 8,constitutes a central axis and the central axis coincides with a readingdirection by the reproducing probe 1 (hereinafter, referred to as atracking direction). That is, a section of the data bit 15 orthogonal tothe reading direction is formed in a shape of a groove in a triangularshape as shown by FIG. 4 and the apex of the triangular shape, that is,a bottom point of the groove is disposed on the central axis of reading(central axis of tracking). By presence of the two symmetrical inclinedfaces, directionalities can be given to fluxes of the reflected andscattered light of the near-field light 11. Further, it is preferablefor providing reflected and scattered light having a sufficientintensity to form a metal reflecting film on the surface of theinformation recording medium 8. Further, the reflection efficiency ofthe near-field light 11 can also be promoted by forming the informationrecording medium 8 per se by a metal.

Accordingly, by arranging a constitution comprising the convergingoptical system 4 and the reproduced light detector 6 and a constitutioncomprising the converging optical system 5 and the reproduced lightdetector 7 at positions symmetrical to each other relative to a centralaxis in parallel with a tracking direction of the very small aperture 2of the reproducing probe 1 (hereinafter, referred to as reproducingprobe central axis), fluxes of the reflected and scattered lightreflected in directions symmetrical with each other by the two inclinedfaces provided at the data bit 15 can be detected.

FIG. 5 is a view for explaining detection of reflected and scatteredlight when the reproducing probe 1 is arranged in a state in which thecentral axis of the reproducing probe and the tracking central axis arenot coincident with each other. In FIG. 5, the reproducing probe 1 isdisposed on the left side of the tracking central axis, that is, thebottom apex of the data bit 15 and fluxes of reflected and scatteredlight 16 and 17 are produced by interaction between the near-field light11 formed at the very small aperture 2 under the state and the data bit15.

In FIG. 5, the near-field light 11 is significantly scattered by theleft inclined face of the data bit 15 and the reflected and scatteredlight 17 is guided in the left direction depending on an angle ofinclination of the left inclined face. The reflected and scattered light17 guided in the right direction is introduced into the convergingoptical system 5 and is inputted to the reproduced light detector 7.

Meanwhile, the near-field light 11 shows the largest intensity on thecentral axis of the reproducing probe and directly under the very smallaperture 2 and accordingly, on the right inclined face of the data bit15 disposed remote from the central axis of the reproducing probe, theintensity of the reflected and scattered light 16 provided by beingscattered becomes weaker than that of the reflected and scattered light17 on the side of the left inclined face. The reflected and scatteredlight 16 guided in the left direction is also introduced into theconverging light optical system 4 and is inputted to the reproducedlight detector 6.

Accordingly, in this case, the electric signal outputted at thereproduced light detector 7 is a signal larger than the electric signaloutputted at the reproduced light detector 6. These electric signals areinputted to the difference circuit 20 and the differential signal isformed there as mentioned above. The magnitude of the differentialsignal indicates a degree of shift of the reproducing probe 1 from thetracking central axis and the differential signal is converted into thetracking signal by being inputted to the tracking signal generator 21.The tracking signal is a signal for driving the actuator 22 and theactuator 22 controls the position of the reproducing probe 1 inaccordance with the tracking signal. For example, when the differencecircuit 20 carries out an operation of subtracting the electric signaloutputted from the reproduced light detector 7 from the electric signaloutputted from the reproduced light detector 6, in a state shown by FIG.5, the differential signal outputted from the difference circuit 20shows a negative value. Successively, the tracking signal generator 21interprets the negative differential signal as a signal for moving theactuator 22 to the right and outputs a tracking signal indicating themoving direction and a moving amount in accordance with the magnitude ofthe differential signal to the actuator 22. That is, the tracking signalgenerator 21 generates an actuator driving signal for correcting theshift between the reproducing probe 1 and the tracking central axis. Theactuator 22 moves the reproducing probe 1 in accordance with thetracking signal outputted from the tracking signal generator 21 andmakes the central axis of the reproducing probe and the tracking centralaxis coincide with each other. That is, tracking control in the rightdirection is carried out.

Further, although in FIG. 5, there is shown the case in which thereproducing probe 1 is disposed on the left side of the tracking centralaxis, when the reproducing probe 1 is disposed on the right side of thetracking central axis, an operation reverse to the above-described iscarried out. That is, in that case, tracking control in the leftdirection is carried out.

Further, in parallel with the above-described tracking processing, theelectric signal outputted at the reproduced light detector 7 and theelectric signal outputted at the reproduced light detector 6 areinputted to the adding circuit 23 where the adding operation is carriedout and are outputted as the reproduced signal. Thereby, presence orabsence of the data bit 15 directly under the very small aperture 2 isdetected.

FIG. 6 is a view for explaining detection of reflected and scatteredlight when the reproducing probe 1 is arranged such that the centralaxis of the reproducing probe and the tracking central axis coincidewith each other. In FIG. 6, the near-field light 11 formed at the verysmall aperture 2 produces fluxes of the reflected and scattered light 16and 17 by uniform interaction of the right inclined face and the leftinclined face of the data bit 15. That is, both of the fluxes of thereflected and scatted light 13 and 14 show substantially the sameintensity and the electric signals respectively outputted at thereproduced light detector 7 and the reproduced light detector 6 alsoshow substantially the same magnitude. Accordingly, no difference isproduced at the difference circuit 20 and positioning control in theactuator 22 is not carried out. That is, FIG. 6 represents a final stateafter the above-described tracking control has been carried out.

Further, although according to Embodiment 2, explained above, there isconstructed the structure in which the inclined faces are provided onthe left and on the right of the tracking central axis by constitutingthe section of the data bit recorded to the information recording mediumby the groove in the triangular shape, for example, there may beconstructed a structure in which the section of the data bit isconstituted by a groove in a semicircular shape and curved faces areprovided on the left and on the right of the tracking central axis.

Further, data may be read by constituting the information recordingmedium in a disk-like shape as in CD and rotating the informationrecording medium at high speed or data may be read by forming theinformation recording medium as a flat plate without being limited tothe disk-like shape and carrying out vector scanning on the reproducingprobe.

As has been explained above, according to the information recordingmedium of Embodiment 2, the data bit constituting the information unitis constructed by a structure in the concave in which the inclined facesor the curved faces are provided symmetrically in the left and rightdirection relative to the central axis of the reading direction(tracking direction) and accordingly, the directionalities can be givento fluxes of the reflected and scattered light produced by scatteringnear-field light by the data bit. Further, according to the informationreproducing apparatus of Embodiment 2, fluxes of the reflected andscattered light provided from the data bit of the above-describedinformation recording medium can be detected in two symmetricaldirections relative to the central axis of the reproducing probe and thetracking control of the reproducing probe can be carried out from thedifference between the two detected signals. Further, the near-fieldlight formed at the very small aperture of the reproducing probe isutilized as a signal for tracking control and accordingly, there isachieved tracking control at high accuracy accompanied by highpositional resolution. Further, the constitution of the apparatus can besimplified since the optical systems used in detecting fluxes of thereproduced signal and detecting the tracking signal are not separatedbut are unified.

Further, a simple apparatus constitution which does not necessitate theconverging optical systems 4 and 5 and the reproduced light detectors 6and 7 can further be realized in the information reproducing apparatusaccording to Embodiments 1 and 2, explained above by particularlyadopting a plane probe 40 of an integral type installed with reproducedlight detectors 41 and 42 symmetrically on both sides of the very smallaperture 2 as shown by FIG. 7, as the reproducing probe 1. The planeprobe 40 can be fabricated by a silicon process used in conventionalsemiconductor fabrication technology and the reproduced light detectors41 and 42 are, for example, photodiodes integrated on a silicon wafer.Further, there can also be constructed a constitution in which thereproduced light detectors 41 and 42 are integrated with opticalwaveguides. According to the plane probe 40, the reflected and scatteredlight which is scattered by the data bit 12 of the convex of theinformation recording medium 3 or by the data bit 15 of the concave ofthe information recording medium 8, mentioned above, with no particularneed of fine adjustment of the positions of the reproduced lightdetectors.

Further, by adopting a plane probe 50 installed with reproduced lightdetectors 43 and 44 for reproduced signals at vicinities of the verysmall aperture 2 of the plane probe 40 as shown by FIG. 8, as areproducing probe, intensities of detecting reproduced signals can becomplemented by detecting reflected and scattered light for tracking bythe reproduced light detectors 41 and 42 and detecting fluxes ofreflected and scattered light for the reproduced signals by thereproduced light detectors 41 and 42 and the reproduced light detectors43 and 44.

(Embodiment 3)

FIG. 9 is a block diagram showing an outline constitution of aninformation reproducing apparatus according to Embodiment 3. In FIG. 9,the information reproducing apparatus according to Embodiment 3 isconstituted by an information recording medium 30 formed with data bitsat high density, a reproducing probe 25 for scattering near-field lightformed at the data bits of the information recording medium 30, theconverging optical systems 4 and 5 for converging fluxes of reflectedand scattered light which are scattered by the reproducing probe 25, thereproduced light detectors 6 and 7 for receiving fluxes of lightconverged by the converging optical systems 4 and 5, the differencecircuit 20 for calculating a difference between respective electricsignals outputted from the reproduced light detectors 6 and 7 andoutputting a differential signal, the tracking signal generator 21 forgenerating and outputting a tracking signal from the differential signaloutputted from the difference circuit 20, the actuator 22 forcontrolling the position of the reproducing probe 25 in accordance withthe tracking signal outputted from the tracking signal generator 21 andthe adding circuit 23 for forming a reproduced signal by adding therespective electric signals outputted from the reproduced lightdetectors 6 and 7.

The information recording medium 30 comprises a light-transmittingmaterial and is formed with a portion locally producing strongnear-field light on its surface by laser beam 33 irradiated from a rearface thereof by a laser beam source (not illustrated) as a data bit 32constituting an information unit. That is, the data bit 32 functions asa very small aperture for forming near-field light and near-field lightaccording to the above-described collection mode can be utilized.Further, the date bit 32 is formed by, for example, piling up a metalthin film on a light-transmitting substrate and removing a portion ofthe metal thin film in correspondence with the data bit 32 or changing arefractive index of a portion of the light-transmitting substrate incorrespondence with the data bit 32, from that of the surrounding.Further, presence or absence of the data bit 32 can also be detected byconstituting the data bit 32 by a fluorescent material and arrangingoptical filters for cutting off the laser beam 33 and transmittingfluorescent light respectively between the converging optical system 4and the reproduced light detector 6 and between the converging opticalsystem 5 and the reproduced light detector 7.

The reproducing probe 25 is formed in a wedge-like shape as shown byFIG. 10 and can scatter near-field light at a front end portion thereof.Particularly, the data bit 32 can optimally be read by constituting acentral axis by a top portion of the reproducing probe 25 which isformed by combining two symmetrical inclined faces constituting thewedge-like shape and making the central axis coincide with the readingdirection by the reproducing probe 25 (hereinafter, referred to astracking direction). That is, a section of the data bit 32 orthogonal tothe direction of reading the data bit 32 is formed by a triangular shapeas shown by FIG. 10 and the apex of the triangular shape is controlledto dispose on a reading central axis (tracking central axis). By thepresence of the two symmetrical inclined faces, directionalities can begiven to fluxes of the reflected and scattered light of the near-fieldlight 31.

The near-field light 31 formed by the data bit 32 of the informationrecording medium 30 is scattered at the front end portion of thereproducing probe 25 and the scattered light constitutes propagatinglight (hereinafter, referred to as reflected and scattered light) and isintroduced into the converging optical systems 4 and 5. In this case,the converging optical systems 4 and 5 each is constructed by aconstitution of a converging lens or a collimating lens or the lensadded with a light guide or an optical fiber and converge fluxes of thereflected and scattered light by the reproduced light detectors 6 and 7such that sufficiently detectably intensities are constituted. Thereproduced light detectors 6 and 7 are, for example, photodiodes orphotomultipliers.

The converging optical systems 4 and 5 and the reproduced lightdetectors 6 and 7 are arranged at fixed positions relative to thereproducing probe 25 and are positioned relative to the informationrecording medium 3 along with the reproducing probe 25 particularly bypositioning control by the actuator 22. Therefore, it is preferable toconstitute a light reproducing head integrated with the reproducingprobe 25, the converging optical systems 4 and 5 and the reproducedlight detectors 6 and 7 and the light reproducing head is subjected topositioning control by the actuator 22.

Accordingly, by arranging a constitution comprising the convergingoptical system 4 and the reproduced light detector 6 and a constitutioncomprising the converging optical system 5 and the reproduced lightdetector 7 at positions symmetrical to each other relative to a centralaxis in parallel with a tracking direction of the front end of thereproducing probe 25 (hereinafter, referred to as reproducing probecentral axis), fluxes of the reflected and scattered light reflected indirections symmetrical with each other by the two inclined facesprovided at the reproducing probe 25 can be detected.

FIG. 11 is a view for explaining detection of reflected and scatteredlight in the case in which the reproducing probe 25 is arranged in astate in which the central axis of the reproducing probe and thetracking central axis are not coincident with each other. In FIG. 11,the reproducing probe 25 is disposed on the left side of the trackingcentral axis, that is, the central axis of the data bit 32 and fluxes ofreflected and scattered light 35 and 36 are produced by interactionbetween the near-field light 31 formed at the data bit 32 under thestate and the reproducing probe 25.

In FIG. 11, the near-field light 31 is significantly scattered by theright inclined face of the reproducing probe 25 and the reflected andscattered light 35 is guided in the right direction depending on anangle of inclination of the right inclined face. The reflected andscattered light 35 guided in the right direction is introduced into theconverging optical system 5 and is inputted to the reproduced lightdetector 7.

Meanwhile, near-field light 31 shows the largest intensity on thecentral axis of the data bit 32 and accordingly, the intensity of thereflected and scattered light 36 provided by being scattered at the leftinclined face of the reproducing probe 25 disposed remote from thecentral axis of the data bit 32, becomes weaker than that of thereflected and scattered light 35 on the side of the right inclined face.The reflected and scattered light 36 guided in the left direction isalso introduced into the converging optical system 4 and is inputted tothe reproduced light detector 6.

Accordingly, in this case, the electric signal outputted at thereproduced light detector 7 is a signal larger than the electric signaloutputted at the reproduced light detector 6. These electric signals areinputted to the difference circuit 20 and the differential signal isformed there as mentioned above. The magnitude of the differentialsignal indicates a degree of shift of the reproducing probe 25 from thetracking central axis and the differential signal is converted into thetracking signal by being inputted to the tracking signal generator 21.The tracking signal is a signal for driving the actuator 22 and theactuator 22 controls the position of the reproducing probe 1 inaccordance with the tracking signal. For example, when the differencecircuit 20 carries out an operation of subtracting the electric signaloutputted from the reproduced light detector 7 from the electric signaloutputted from the reproduced light detector 6, in a state shown by FIG.11, the differential signal outputted from the difference circuit 20shows a negative value. Successively, the tracking signal generator 21interprets the negative differential signal as a signal for moving theactuator 22 to the right and outputs a tracking signal indicating themoving direction and a moving amount in accordance with the magnitude ofthe differential signal to the actuator 22. That is, the tracking signalgenerator 21 generates an actuator driving signal for correcting theshift between the reproducing probe 25 and the tracking central axis.The actuator 22 moves the reproducing probe 25 in accordance with thetracking signal outputted from the tracking signal generator 21 andmakes the central axis of the reproducing probe and the tracking centralaxis coincide with each other. That is, tracking control in the rightdirection is carried out.

Further, although in FIG. 11, there is shown the case in which thereproducing probe 25 is disposed on the left side of the trackingcentral axis, when the reproducing probe 25 is disposed on the rightside of the tracking central axis, an operation reverse to theabove-described is carried out. That is, in that case, tracking controlin the left direction is carried out.

Further, in parallel with the above-described tracking processing, theelectric signal outputted at the reproduced light detector 7 and theelectric signal outputted at the reproduced light detector 6 areinputted to the adding circuit 23 where the adding operation is carriedout and are outputted as the reproduced signal. Thereby, presence orabsence of the data bit 32 directly under the very small aperture 2 isdetected.

FIG. 12 is a view for explaining detection of reflected and scatteredlight when the reproducing probe 25 is arranged such that the centralaxis of the reproducing probe and the tracking central axis coincidewith each other. In FIG. 12, the near-field light 31 formed at the databit 32 produces fluxes of the reflected and scattered light 35 and 36 byuniform interaction of the right inclined face and the left inclinedface of the data bit 32. That is, both of the fluxes of the reflectedand scatted light 35 and 36 show substantially the same intensity andthe electric signals respectively outputted at the reproduced lightdetector 7 and the reproduced light detector 6 also show substantiallythe same magnitude. Accordingly, no difference is produced at thedifference circuit 20 and positioning control in the actuator 22 is notcarried out. That is, FIG. 12 represents a final state after theabove-described tracking control has been carried out.

Further, according to Embodiment 3, explained above, data may be read byconstituting the information recording medium in a disk-like shape as inCD and rotating the information recording medium at high speed or datamay be read by forming the information recording medium as a flat platewithout being limited to the disk-like shape and carrying out vectorscanning on the reproducing probe.

As has been explained above, according to the information reproducingapparatus of Embodiment 3, the near-field light formed at the data bitof the information recording medium is scattered by the reproducingprobe in the wedge-like shape and fluxes of the reflected and scatteredlight provided thereby can be detected in two directions which aresymmetrical relative to the central axis of the reproducing probe andtracking control of the reproducing probe can be carried out by thedifference between the two detected signals. Further, the near-fieldlight formed at the data bit of the information recording medium isutilized as a signal for tracking control and accordingly, there can beachieved the tracking control at high accuracy accompanied by highpositional resolution. Further, the apparatus constitution can besimplified since the optical systems used in detecting fluxes of thereproduced signal and detecting the tracking signal are not separatedbut are unified.

INDUSTRIAL APPLICABILITY

As has been explained, according to the invention, the unit ofinformation is constructed by the structure in which the inclined facesor the curved faces are provided symmetrically in the left and rightdirection with the reading direction as the central axis andaccordingly, the directionalities can be given to the fluxes ofreflected light reflected when the unit of information is irradiatedwith light and the difference between the intensities of the fluxes ofreflected light can be utilized as a signal for tracking.

Further, according to the invention, the section of the unit ofinformation orthogonal to the reading direction is formed in thetriangular shape and accordingly, when the unit of information isirradiated with light, the light can efficiently be reflected at theinclined faces of the unit of information, further, the directionalitiescan be given to fluxes of the reflected light and accordingly, thedifference between the intensities of the fluxes of reflected light canbe utilized as a signal for tracking.

Further, according to the invention, the section of the unit ofinformation orthogonal to the reading direction is formed in thesemicircular shape and accordingly, when the unit of information isirradiated with light, the light can efficiently be reflected at thecurved faces of the unit of information, further, the directionalitiescan be given to fluxes of the reflected light and accordingly, thedifference between the intensities of the fluxes of reflected light canbe utilized as a signal for tracking.

Further, according to the invention, the unit of information isconstructed by the structure in which the unit of information isprovided with the inclined faces or the curved faces symmetrically inthe left and right direction with the reading direction as the centralaxis and is formed in the convex relative to the surface of theinformation recording medium and accordingly, when the unit ofinformation is irradiated with light which is shifted to the left, thelight can be reflected strongly in the left direction, when the unit ofinformation is irradiated with light which is shifted to the right, thelight can be reflected strongly to the right direction and accordingly,the difference between the intensities of fluxes of the reflected lightcan be utilized as a signal for tracking.

Further, according to the invention, the unit of information isconstructed by the structure in which the unit of information isprovided with the inclined faces or the curved faces symmetrically inthe left and right direction with the reading direction as the centralaxis and is formed in the concave relative to the surface of theinformation recording medium and accordingly, when the unit ofinformation is irradiated with light which is shifted, to the left side,the light can be reflected strongly in the right direction, when theunit of information is irradiated with light which is shifted to theright side, the light can be reflected strongly in the left directionand accordingly, the difference between the intensities of fluxes of thereflected light can be utilized as a signal for tracking.

Further, according to the invention, the metal reflecting film is formedon the surface of the information recording medium and accordingly,light irradiated to the unit of information can efficiently bereflected.

Further, according to the invention, by forming the information unitconstructed by the structure in which the inclined faces or the curvedfaces are provided on the left and on the right with the readingdirection as the central axis and with the central axis as the topportion, to the information recording medium and making the near-fieldlight formed at the very small aperture of the reproducing probeincident on the unit of information, fluxes of the reflected andscattered light provided with the directionalities to the left and tothe right can be formed, the fluxes of reflected and scattered light aredetected at at least two positions symmetrical with each other relativeto the central axis of the very small aperture and the position of thereproducing probe is controlled in accordance with the detected signaland accordingly, tracking control with high accuracy utilizing thenear-field light can be carried out.

Further, according to the invention, by forming the information unitconstructed by the structure in which the inclined faces or the curvedfaces are provided on the left and on the right with the readingdirection as the central axis and with the central axis as the topportion, to the information recording medium and making the near-fieldlight formed at the very small aperture of the reproducing probeincident on the information unit, there can be formed fluxes of thereflected and scattered light provided with the directionalities to theleft and to the right, the fluxes of reflected and scattered light aredetected by the first and the second light detecting means arranged atat least two positions symmetrical with each other relative to thecentral axis of the very small aperture, the differential signalindicating the difference between the first detected signal detected andoutputted by the first light detecting means and the second detectedsignal detected and outputted by the second light detecting means, isformed by the difference calculating means, position control of thereproducing probe in accordance with the differential signal can becarried out by the reproducing probe position controlling means andaccordingly, tracking control with high accuracy utilizing thenear-field light can be carried out. Further, the reproduced signal canbe formed by carrying out the operation of adding the first detectedsignal and the second detected signal by the reproduced signal formingmeans and accordingly, the information can simultaneously be reproduced.

Further, according to the invention, as the reproducing probe, there canbe utilized the probe of the optical fiber type used in the conventionalnear-field microscope and accordingly, the accumulated technology of thenear-field microscope can effectively be applied to the informationreproducing apparatus.

Further, according to the invention, as the reproducing probe, there canbe utilized the probe of the cantilever-type used in the conventionalnear-field microscope and accordingly, the accumulated technology of thenear-field microscope can effectively be applied to the informationreproducing apparatus.

Further, according to the invention, as the reproducing probe, there canbe utilized the plane probe arranged with the first and the second lightdetecting means and accordingly, the simple apparatus constitution canbe realized with no need of adjusting the positions of the first and thesecond light detecting means.

Further, according to the invention, as the reproducing probe, there canbe utilized the plane probe arranged with the first and the second lightdetecting means and further with the third and the fourth lightdetecting means for detecting the fluxes of reflected and scatteredlight at vicinities of the very small aperture and accordingly, thereproduced signal having further sufficient intensity can be detected bythe first and the second light detecting means and the third and thefourth light detecting means.

Further, according to the invention, the near-field light produced atthe unit of information of the information recording medium is scatteredby the reproducing probe, fluxes of the reflected and scattered lightare detected at at least two positions symmetrical with each otherrelative to the front end portion of the reproducing probe, the positionof the reproducing probe is controlled in accordance with the detectedsignal and accordingly, tracking control with high accuracy utilizingthe near-field light can be carried out.

Further, according to the invention, the near-field light produced atthe unit of information of the information recording medium is scatteredby the reproducing probe, fluxes of the reflected and scattered lightare detected by the first and the second light detecting means arrangedat at least two position symmetrical with each other relative to thecentral axis of the very small aperture, the differential signalindicating the difference between the first detected signal detected andoutputted by the first light detecting means and the second detectedsignal detected and outputted by the second light detecting means isformed by the difference calculating means, the position control of thereproducing probe in accordance with the differential signal can becarried out by the reproducing probe position controlling means andaccordingly, tracking control with high accuracy utilizing thenear-field light can be carried out. Further, the reproduced signal canbe formed by carrying out the operation of adding the first detectedsignal and the second detected signal by the reproduced signal formingmeans and accordingly, the information can simultaneously be reproduced.Further, according to the invention, the reproducing probe is formed inthe wedge-like shape and accordingly, by reflecting the near-field lightproduced at the unit of information of the information recording mediumby the two inclined faces constituting the wedge-like shape, thedirectionalities can be given to fluxes of the reflected light andaccordingly, the difference between the intensities of the fluxes ofreflected light can be provided further significantly and trackingcontrol with high accuracy having high reliability utilizing thenear-field light can be carried out. Further, the reproduced signal canbe provided with sufficiently large intensity by the reflected light.

What is claimed is:
 1. An information recording medium from whichinformation is read by a reproducing probe having a very small aperturefor forming near-field light on a surface of the recording medium, theinformation recording medium comprising: a substrate; and a plurality ofunits of information provided on the substrate, the units of informationbeing non-fluorescent and uncharged, and comprising inclined or curvedfaces formed on the substrate and provided symmetrically in a left andright direction relative to a reading direction of the information, theleft and right inclined or curved faces being directly joined to eachother at a central axis without a flat face being interposedtherebetween.
 2. The information recording medium according to claim 1;wherein the units of information have a triangular cross-sectional shapein a direction orthogonal to the reading direction.
 3. The informationrecording medium according to claim 1; wherein the units of informationhave a semicircular cross-sectional shape in a direction orthogonal tothe reading direction.
 4. The information recording medium according toclaim 2 or 3; wherein the units of information have a convex shaperelative to a surface of the substrate.
 5. The information recordingmedium according to claim 2 or 3; wherein the units of information havea concave shape relative to a surface of the substrate.
 6. Theinformation recording medium according to claim 2 or 3; furthercomprising a reflective metal film formed on a surface of the substrate.7. An information reproducing apparatus for reproducing information by areproducing probe provided with a very small aperture for formingnear-field light, characterized in comprising: an information recordingmedium in which a unit of the information is constructed by a structurein which inclined faces or curved faces are provided symmetrically in aleft and right direction relative to a reading direction, and the leftand the right inclined faces intersect with each other or the left andthe right curved faces coincide with each other; and a control apparatusfor detecting fluxes of reflected and scattered light produced byscattering the near-field light by the unit of the information at atleast two positions symmetrical with each other relative to a centralaxis of the very small aperture along the reading direction andcontrolling a position of the reproducing probe in accordance with adetected signal.
 8. An information reproducing apparatus for reproducinginformation by a reproducing probe provided with a very small aperturefor forming near-field light, characterized in comprising: aninformation recording medium in which a unit of the information isconstructed by a structure in which inclined faces or curved faces areprovided symmetrically in a left and right direction relative to areading direction and the left and the right inclined faces intersectwith each other or the left and the right curved faces coincide witheach other; and a first and a second light detecting means arrangedsymmetrically with each other in the left and right direction relativeto a central axis of the very small aperture along the reading directionfor detecting fluxes of reflected and scattered light produced byscattering the near-field light by the unit of the information andoutputting detected signals; difference calculating means forcalculating a difference between a first detected signal outputted fromthe first light detecting means and a second detected signal outputtedfrom the second light detecting means and outputting a differentialsignal; reproducing probe position controlling means for controlling aposition of the reproducing probe in accordance with the differentialsignal; and reproduced signal forming means for calculating to add thefirst detected signal and the second detected signal and forming areproduced signal.
 9. The information recording apparatus according toclaim 7 or 8, characterized in that the reproducing probe comprises anoptical fiber provided with the very small aperture at a front endthereof.
 10. The information reproducing apparatus according to claim 7or 8, characterized in that the reproducing probe is a probe of acantilever type provided with the very small aperture at a projectedportion thereof.
 11. The information recording apparatus according toclaim 7 or 8, characterized in that the reproducing probe is a planeprobe comprising a plane substrate formed by being penetrated with ahole in a shape of an inverse cone to constitute the very small apertureby a top portion thereof and the first and the second light detectingmeans are arranged at the plane substrate.
 12. The informationreproducing apparatus according to claim 11, characterized in that thereproducing probe is the plane probe arranged with a third and a fourthlight detecting means for detecting the fluxes of the reflected andscattered light at vicinities of the very small aperture.
 13. Aninformation reproducing apparatus comprising: a reproducing probe forforming near-field light at an information recording medium having aplurality of units of information formed thereon, the information beingreproduced by scattering of the near-field light by the units ofinformation; light detecting means for detecting fluxes of reflected andscattered light produced by scattering of the near-field light by theunits of information formed on the information recording medium at atleast two positions symmetrical with each other relative to a front endportion of the reproducing probe; and means for controlling a positionof the reproducing probe in accordance with the detected light fluxes.14. An information reproducing apparatus for forming near-field light atan information recording medium and reproducing information by areproducing probe for scattering the near-field light, characterized incomprising: a first and a second light detecting means arrangedsymmetrically with each other relative to a front end portion of thereproducing probe along a reading direction for detecting fluxes ofreflected and scattered light produced by scattering the near-fieldlight by a front end portion of the reproducing probe and outputtingdetected signals; difference calculating means for calculating adifference between a first detected signal outputted from the firstlight detecting means and a second detected signal outputted from thesecond light detecting means and outputting a differential signal;reproducing probe position controlling means for controlling a positionof the reproducing probe in accordance with the differential signal; andreproduced signal forming means for forming a reproduced signal bycalculating to add the first detected signal and the second detectedsignal.
 15. The information reproducing apparatus according to claim 13or 14, characterized in that the reproducing probe is formed in awedge-like shape.